1. Field of the Invention
The present invention is generally related to imagery display systems and more specifically to an apparatus and method for increasing the resolution of a wide angle virtual reality display by projecting alternate image source frames onto different respective halves of the user's field of view, thereby expanding the field of view.
2. Review of the Prior Art
In a wide angle virtual reality or head mounted display, if the image source is made up of one unit (e.g. one CRT or one liquid crystal display), as is generally the case due to economics and scarcity of space, then for either an increased angular extent in the vertical or horizontal display, the fixed number of image source pixels must be "stretched" over an increased angular swath. For displays over 35.degree. in angular extent this may create substantial granularity.
For instance, in the case of a virtual reality display, it may be desirable to show the viewer imagery over a horizontal angular extent of 40.degree. in order to create a more realistic display. If this imagery is originated on an image source of limited width, however, and is then "stretched" to over 40.degree. in angle, image granularity will result since the spacing between adjacent pixels will become noticeable.
For systems which store the imagery with a greater density of pixels than can be represented on a currently available image source screen, the single image source will prevent a display with enough pixel density to avoid the problem of granularity even though more information is available. Unfortunately, space and weight restraints may preclude the introduction of a second image source into the system.
One potential solution for this problem would be to display separately the left and right portions of the imagery in greater detail, alternately on the image source and then route these, alternately, to the viewer's left and right halves of field of view. The image persistency of the human eye would prevent the imagery from appearing "choppy."
Unfortunately, until now there has been no quick and easily controllable mechanism for switching an image from one path to another with precise timing. For the application just described, the switching must be accomplished at times on the order of 10 milliseconds. Mechanical system rarely work this quickly without enormous penalties in complexity and cost. Further, there is no discrete electrical component which performs the same function as a mirror which can be "toggled" between positions.
3. Prior Art References
Most of the prior art concerned with alternating imagery deals with stereoscopic displays. Because the problems encountered in that field are not the same as those described in the previous section, the prior art is inapposite.
In stereoscopic display systems, slightly different imagery must be provided to each eye. This is generally accomplished by sending a sequential series of alternating images for the right and left eyes and blocking each image from reaching the wrong eye. There is no necessity, however, to break the imagery up into different paths.
For example, U.S. Pat. No. 4,632,508, to Connelly, shows a device for presenting both of the viewer's eyes with coordinated imagery. This device, however, uses two separate image sources. This could be cumbersome, especially in an aircraft cockpit area already filled with equipment.
U.S. Pat. No. 4,281,341, to Byatt, discloses a stereoscopic television system which alternately produces horizontally and vertically polarized images. The viewer is provided with glasses that have one horizontally polarized lens and one vertically polarized lens. Each eye, therefore, receives only those images which correspond to that eye's perspective. This system, however, could not work for different fields of view. It does not reroute and change the angle of the images. Moreover, since there is no collimation, the images are not presented at virtual infinity.
The patent to Hatano et al., U.S. Pat. No. 5,071,230, discloses a liquid crystal display device. An image is formed by controlling LC grids and may be displayed on a screen using a beam-splitter and a lens. There is no effort here to direct the imagery to more than one path.
U.S. Pat. No. 4,954,890, to Park, projects distinctly polarized right and left eye images onto a screen to be read separately by the viewer's right and left eye equipped with appropriately polarized lenses. There is no effort to display information in different portions of the field of view.
U.S. Pat. No. 5,007,715, to Verhulst, discloses another stereoscopic display system. Although, an image generating system that is different than that of Byatt is used, the general technique is the same, with images produced that are toggled between one polarization and another. The viewer wears glasses in which the lenses are polarized in a mutually orthogonal manner.
In the patent to Bosserman, U.S. Pat. No. 4,361,384, a high luminance miniature display is taught. This device does not address the problem of how to switch imagery from one path to another. Rather, it addresses how to achieve a bright display in a very small area.
In the patent to Kalmanash, U.S. Pat. No. 4,877,307, a stereoscopic display system which utilizes circular polarization is disclosed. A liquid crystal cell introduces a controllable relative phase shifts between orthogonal light components, resulting in circular polarization with one of two predetermined directions of rotation. Each lens of the associated viewing glasses transmits only that circularly polarized light with a specific predetermined direction of rotation. By interleaving right eye and left eye images on the image source and alternately polarizing them with right hand and left hand circular polarization, a stereoscopic image is created for a user wearing the viewing glasses which transmit the right eye images to the right eye and the left eye images to the left eye.
U.S. Pat. No. 4,897,715, to Beamon III, is yet another stereoscopic viewing device. It has two different image forming devices, but, it does not address the problem of how to use one image source to obtain two different sets of images corresponding to two different parts of the field of view.
In U.S. Pat. No. 4,755,023, to Evans et al., (assigned to the assignee of the present invention) a headgear mounted display visor is shown which has a particularly beneficial shape and desirable characteristics. This reference does not consider the issue of sending imagery along a selectable path.
In a later patent to Evans et al., U.S. Pat. No. 4,761,056 (assigned to the present assignee) a Compact Helmet Mounted Display is taught which projects an image from a source to the eye along a fixed path.